In June 1950 the North's army drove south, captured Seoul and routed a makeshift American task force sent from Japan to help the southerners. General MacArthur, remote in his Tokyo headquarters, invoked reinforcements from UN member states and Britain responded. Some courageous decisions were made by Labour's Clement Attlee, Foreign Secretary Ernest Bevin and Defence Minister Emmanuel Shinwell (who years later revealed that key decisions - to support UN action in Korea, increase defence expenditure all round, and finally to go nuclear with the creation of the RAF's V- Force - were actually taken out of Cabinet, many of its members, though staunch fellow members of the Labour movement, nurturing sympathies "closer to the Vistula than the Thames".)
This was the UN's first test of resolve, the first coalition war fought under a nuclear threat - an American one, that is, for the Russians had yet to detonate their first bomb - and the first in which jet aircraft played a major role. US Air Force commanders unleashed their B-29 Superfortresses on North Korea, flattening its industrial and transportation infrastructure. Instead of demoralising the civil population it hardened their resolve, as in the 3rd Reich and again in Vietnam. Air power alone cannot secure victory; in the end, only troops can take and hold ground.
Initial UN reverses were met by MacArthur's masterstroke, landing in the enemy's rear at Inchon in September 1950. This should have crowned the old general's career but his ambition got the better of him; he pursued the enemy back across the 38th into the north until the Chinese, unsurprisingly nervous at the approach of the triumphant UN forces, hurled them back south of Seoul.
A weary campaign occupied the rest of the first terrible winter. A strong (but scratch) British brigade came to join the two Hong Kong battalions which had been there since the previous August. Soon, a Canadian brigade arrived; in mid-1951 a splendid Commonwealth Division was formed. There were now combat troops from Britain, Australia and New Zealand, a superb field ambulance unit from India, a South African fighter squadron, and contingents from Turkey, Belgium, Holland, Greece, France, Ethiopia, Colombia, the Philippines and Thailand. Many of these also provided ships as well. But the US bore the brunt in terms of blood, equipment and administrative support.
The British active army of 1950 was some 350,000 men strong but, as most of these were conscripts too young to serve in combat, recourse had to be made to dragging reservists back to the colours, unenthused by the prospect of laying down their lives in a distant country for a cause they little comprehended. As it was, over a thousand Britons failed to return and lie buried on Korean soil. Those who returned received a modest "Korean War Bounty" but no post-traumatic stress counselling, which had yet to be invented, and it would be over 30 years before a memorial was unveiled, at the expense of surviving veterans, in St Paul's Cathedral.
It remains a forgotten war but it was one in which at least two million, soldiers and civilians, died; and it is now as far behind in the wake of history as was the Boer War to those who mobilised at Colchester and on Salisbury Plain in that distant hot summer of 1950.
Michael Hickey is the author of `The Korean War: the West confronts Communism, 1950-53' (John Murray, pounds 25)